A spoked bicycle wheel comprises a peripheral crown or rim for assembling a tire, a central hub to be rotationally assembled on the bicycle frame and a plurality of spokes extending between the rim and the hub.
A bicycle spoke has an elongated body having two ends. In order to be able to assemble the spoke tensioned between the hub and the rim, each of the two ends has a head transversally projecting from the elongated body or else a threading. Typically, an end of the spoke has a projecting head and the opposite end has an outer threading. This configuration is, indeed, preferable since, whereas the end of the spoke provided with the head engages in a suitably shaped seat, on the side of the hub or of the rim, respectively, the screwing depth of the threaded end in an internally threaded seat hole on the side of the rim or of the hub, respectively, allows the fine adjustment of the spoke tension during the assembly step and in the use of the bicycle.
A first type of spoke commonly used is made of steel. The threaded end has a diameter on the order of 2–3 mm. A second type of spoke commonly used is made of aluminum. In this case, the threaded end must have a diameter on the order of 4–6 mm to have characteristics of mechanical strength equal to those of a steel spoke.
Bicycle rims shaped as a single channel are known, with the side walls or fins of which the beads of the tire are coupled through lips protruding from the fins, and on the bottom of which a plurality of seat holes for the attachment of the spokes are made. Rims of such a type have little structural stiffness and thus greater deformability from lateral loads.
To increase the structural stiffness and reduce the deformability from lateral loads, bicycle rims are also known whose cross section defines a radially outer circumferential channel for coupling with a tire and an essentially hollow radially inner circumferential body region, hereafter referred to as “spoke attachment chamber”. The tire coupling channel and the body region are separated by a wall referred to in the field and hereafter as “upper bridge”.
Whereas the channel is subject to standards or restrictions in shape and tolerance in view of its coupling with the tire, the radially inner region can have the most various configurations, provided that it offers an attachment surface for the spokes that is suitable in shape and orientation with respect to the axis of the wheel.
Typical configurations of a bicycle rim of this second known type include an upturned A-shaped cross section, i.e. where the radially inner body region is formed from a single chamber, defined by the upper bridge, two side walls and a radially inner circumferential wall, also referred to as “lower bridge”. The chamber can have an essentially rectangular cross section, i.e. wherein the side walls are substantially parallel to the middle plane of the rim, essentially trapezoidal, symmetrical with respect to the middle plane of the rim, i.e. in which the side walls are oblique, or else asymmetrical, essentially trapezoidal, i.e. wherein a first side wall substantially extends in a plane parallel to the middle plane of the rim and a second wall extends obliquely. In other configurations, the radially inner region is provided with one or more partition walls, extending substantially parallel to the upper bridge or substantially normal to it, so as to define two or more circumferential spoke attachment chambers.
Rims of this type can be made by casting of carbon fiber or by extrusion, calandering and joining the ends of a metallic profile, typically made of aluminum.
The seat holes in the rim and in the hub of a wheel can be configured for direct attachment of the spoke, by respectively having an inner threading for engagement of the threaded end of the spoke, or a shaping matching the projecting head of the spoke, as a seat for engagement thereof. However, more typically a spoke attachment element is used with the spoke and a seat hole at the rim and/or the hub.